Telescope and binoculars

ABSTRACT

A telescope or binoculars includes an erecting system having a plurality of reflecting surfaces. First and second reflecting surfaces and third and fourth reflecting surfaces respectively face each other at right angles. An intersection line between extended surfaces of the first and second reflecting surfaces is perpendicular to the intersection line between extended surfaces of the third and fourth reflecting surfaces. An objective lens is located between the second and third reflecting surfaces and converges object light that is reflected by the first and second reflecting surfaces for forming an image. An eyepiece is located between the fourth reflecting surface and an eye point to magnify the image formed by the objective lens.

BACKGROUND OF THE INVENTION

The present invention relates to a visual optical device such as atelescope or binoculars that has an objective lens, an erecting systemand eyepiece.

A visual optical device that includes an objective lens having apositive refractive power and an eyepiece having a positive refractivepower requires an erecting system that erects an inverted real imageformed by the objective lens when the device is used for a terrestrialobservation.

Therefore, a visual optical device has the erecting system such as apentagonal roof prism or Porro prisms located between the objective lensand the eyepiece. An inverted real image formed by the objective lens iserected by the erecting system, and then the eyepiece magnifies theerected real image for an observation by a naked eye.

Since manufacturing of roof surfaces of a pentagonal roof prism requiresvery high processing accuracy, a manufacturing cost becomes higher,which raises the total cost of the visual optical device. Therefore, thePorro prism erecting system is preferable to be used in the visualoptical device.

FIG. 11 is a developed diagram of an optical system of a conventionalvisual optical device. The optical system 100 of this device consists ofan objective lens 110, an erecting system 130 and an eyepiece 120,arranged in this order from an object side.

The erecting system 130 is a Porro prism erecting system that isprovided with a first Porro prism and a second Porro prism. Each of thePorro prisms is a 45-90-45° reflecting prism whose reflecting surfacesform a right angle for reflecting the light beam through a total angleof 180°. The four reflecting surfaces of the Porro prism erecting systemcan be replaced with mirrors. In the specification, a Porro typeerecting system means both of the Porro prism erecting system and thecombination of alternative mirrors.

It should be noted that the first and second Porro prisms are shown asboxes 131 and 132 illustrated by dotted lines in FIG. 11. The boxes 131and 132 represent spaces occupied by the first and second Porro prisms,respectively.

Object light incident on the optical system 100 from the left-hand sidein FIG. 11 is converged by the objective lens 110 to form a real imageof an object. Since the light reflected by four times through the firstand second Porro prisms, an erected real image is formed on a field top140. The eyepiece 120 magnifies the erected real image.

The maximum incident angle ω is determined by the following equation:

ω=tan⁻¹(y/f _(o))

where y is a radius of aperture of the field stop 140 and f_(o) is afocal length of the objective lens 110. A real field of view is twicethe maximum incident angle, i.e., 2ω.

Since observing region becomes broader as the real field of view 2ωincreases, it is preferable to increase the real field of view. Theequation teaches two ways to increase the real field of view 2ω. A firstway is to decrease the focal length f_(o) of the objective lens 110. Asecond way is to increase the radius of aperture y of the field stop140.

However, if the focal length f_(o) of the objective lens 110 becomesshorter without changing the radius of aperture y, the distance betweenthe objective lens 110 and the field stop 140 becomes too short tolocate the erecting system 130, as shown in FIG. 12.

On the other hand, if the radius of aperture y of the field stop 140becomes larger without changing the space for the erecting system 130,the diameter of the eyepiece must be large as shown in FIG. 13. Theerecting system 130 also becomes larger, which increases the total sizeof the device.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a visualoptical device such as a telescope and binoculars capable of increasingthe real field of view with employing a Porro type erecting system andkeeping a compact total size.

For the above object, according to the present invention, there isprovided an improved telescope, which includes a Porro type erectingsystem having first, second, third and fourth reflecting surfaces thatare arranged from an object side, an objective lens that is locatedbetween the second and third reflecting surfaces, and an eyepiece thatis located between the fourth reflecting surface and an eye point. Theeye point means a position of an exit pupil of the telescope.

The first and second reflecting surfaces and the third and fourthreflecting surfaces are faced to each other at a right angle,respectively. Further, an intersection line between extended surfaces ofthe first and second reflecting surfaces is perpendicular to anintersection line between extended surfaces of the third and fourthreflecting surfaces at twisted positions. The objective lens has apositive refractive power to converge object light that is reflected bythe first and second reflecting surfaces for forming an image and theeyepiece has a positive refractive power to magnify the image formed bythe objective lens.

With this construction, since the objective lens is located between thesecond and third reflecting surfaces, the distance between the objectivelens and a field stop can be shorter than the conventional opticalsystem, which enables to decrease the focal length of the objective lenswithout narrowing the space for the erecting system.

Therefore, a real field of view can be larger with employing the Porrotype erecting system and keeping a compact total size.

The first and second reflecting surfaces may be formed on separatemirrors or formed as back-surfaces of a right-angle prism. When thefirst and second reflecting surfaces are formed as back-surfaces of thesame prism, adjustment between these reflecting surfaces becomesunnecessary, which eases the assembling of the reflecting surfaces ontothe telescope.

In the same manner, the third and fourth reflecting surfaces may beformed on separate mirrors or formed as back-surfaces of a right-angleprism. If the first and second reflecting surfaces, and the third andfourth reflecting surfaces are formed as right angle prisms,respectively, these reflecting surfaces constitute a type I Porro prismerecting system.

According to an another aspect of the present invention, there isprovided a telescope, which includes: a Porro type erecting system whosefirst reflecting surface is formed on a retractable mirror that canswing between a working position where the first and second reflectingsurfaces are perpendicular and a retracted position where the free endof the retractable mirror moves close to the second reflecting surface,an objective lens that is located between the first reflecting surfaceand the fourth reflecting surface, and an eyepiece that is locatedbetween the fourth reflecting surface and an eye point.

With this construction, since the objective lens is located between thefirst reflecting surface and the fourth reflecting surface, the opticalsystem of the telescope becomes thinner when the retractable mirror isin the retracted position.

Further, an angle adjusting mechanism may be added to the retractingmechanism for the retractable mirror in order to finely adjust thedirection of the object light reflected by the retractable mirror. It ispreferable that an incident optical axis, which is an optical axis ofthe objective lens bent by the reflecting surfaces between the objectand the objective lens, are parallel to an exit optical axis, which isan optical axis of the eyepiece extended toward the eye point.

Binoculars of the invention is provided with the above describedtelescopes in a pair. Each of the telescopes includes the Porro typeerecting system, the objective lens located between the second and thirdreflecting surfaces, and an eyepiece located between the fourthreflecting surface and an eye point.

The first reflecting surfaces of the pair of telescopes may be formed ona common mirror. Further, the first reflecting surfaces may be formed onthe retractable mirrors. In the specific case, the first reflectingsurfaces are formed on a common retractable mirror.

The second reflecting surfaces are preferably adjacent to each other inthe same plane. Further, the second reflecting surfaces may be formed ona common mirror.

DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 is a perspective view of an optical system showing arrangement ofoptical elements of binoculars according to a first embodiment;

FIG. 2 is a perspective view of an optical system showing arrangement ofoptical elements of binoculars according to a second embodiment;

FIG. 3 is a side view of the optical system of FIG. 2 when a retractablemirror is in a working position;

FIG. 4 is a side view of the optical system of FIG. 2 when a retractablemirror is in a retracted position;

FIG. 5 is a perspective view of an optical system showing arrangement ofoptical elements of binoculars according to a third embodiment;

FIG. 6 is a side view of the optical system of FIG. 5 when a retractablemirror is in the working position;

FIG. 7 is a view of the optical system of FIG. 5 when a retractablemirror is in the retracted position;

FIG. 8 is a perspective view of an optical system showing arrangement ofoptical elements of binoculars according to a fourth embodiment;

FIG. 9 is a side view of the optical system of FIG. 8 when a retractablemirror is in the working position;

FIG. 10 is a side view of the optical system of FIG. 8 when aretractable mirror is in the retracted position;

FIG. 11 is a developed diagram of an optical system of a conventionalvisual optical device;

FIG. 12 is the developed diagram when a focal length of an objectivelens becomes shorter; and

FIG. 13 is the developed diagram when a radius of aperture of a fieldstop becomes larger.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

FIG. 1 shows an optical system of binoculars according to a firstembodiment of the invention. The binoculars is provided with a pair oftelescopes 1 and 2 arranged side by side for respective eyes of a user.

The binoculars has the Keplerian telescopes 1 and 2 that consist ofobjective lenses 5, 6 to form inverted real images and eyepieces 9, 10to magnify the real images, and Porro prism erecting systems that erectthe inverted real images formed by the objective lenses 5, 6. The Porroprism erecting systems have first Porro prisms 3, 4 and second Porroprisms 7, 8.

Each of the objective lenses 5, 6 and the eyepieces 9, 10 may be asingle lens or a combination of a plurality of lens groups. In any way,the objective lenses 5, 6 and the eyepieces 9, 10 have positiverefractive power, respectively.

The eyepieces 9 and 10 of the telescopes 1 and 2 are arranged such thatthe optical axes thereof are separated in parallel. The distance betweenthe optical axes of the eyepieces 9 and 10 is substantially equal to anaverage interpupillary distance. In the following description, a planein which the optical axes of the eyepieces are located is referred to asa horizontal plane, a direction perpendicular to the horizontal plane isreferred to as a vertical direction, and a direction perpendicular tothe optical axes of the eyepieces in the horizontal plane is referred toas a horizontal direction.

The erecting system has first, second, third and fourth reflectingsurfaces that are arranged from an object side. The first and secondreflecting surfaces and the third and fourth reflecting surfaces arefaced to each other at a right angle, respectively. In the firstembodiment, the reflecting surfaces are back-surfaces of the prisms.That is, the back-surfaces of the first Porro prisms 3 and 4 are thefirst reflecting surfaces 3 a, 4 a and the second reflecting surfaces 3b, 4 b, the back-surfaces of the second Porro prisms 7 and 8 are thethird reflecting surfaces 7 a, 8 a and the fourth reflecting surfaces 7b, 8 b.

Each of the first and second Porro prisms 3, 4, 7 and 8 is a 45-90-45°reflecting prism whose two reflecting surfaces form a right angle forreflecting the light beam through a total angle of 180°. The corners ofthe prism are rounded to minimize breakage and simplify assembly. Thefirst and second Porro prisms 3, 4 and 7, 8 are arranged as type I Porroprism erecting systems. Namely, an intersection line between extendedsurfaces of the reflecting surfaces 3 a, 3 b of the first Porro prism 3is perpendicular to an intersection line between extended surfaces ofthe reflecting surfaces 7 a, 7 b of the second Porro prism 7 at twistedpositions. In the same manner, an intersection line between extendedsurfaces of the reflecting surfaces 4 a, 4 b of the first Porro prism 4is perpendicular to an intersection line between extended surfaces ofthe reflecting surfaces 8 a, 8 b of the second Porro prism 8 at twistedpositions.

The second Porro prisms 7 and 8 are arranged such that the third andfourth reflecting surfaces 7 a, 8 a and 7 b, 8 b are perpendicular tothe horizontal plane. The eyepieces 9 and 10 are located between thefourth reflecting surfaces 7 b, 8 b and eye points. The optical axes ofthe eyepieces 9 and 10 intersect the centers of the fourth reflectingsurfaces 7 b and 8 b at 45° and are bent by a right angle toward thethird reflecting surfaces 7 a and 8 a. The optical axes bent by thefourth reflecting surfaces 7 b and 8 b are again bent by the thirdreflecting surfaces 7 a and 8 a at a right angle in the horizontalplane. Therefore, the optical axes of the eyepieces 9 and 10 are bent by180° in the horizontal plane.

The objective lenses 5 and 6 are located between the second reflectingsurfaces 3 b, 4 b and the third reflecting surfaces 7 a, 8 a, i.e.,between the first Porro prisms 3, 4 and the second Porro prisms 7, 8.The optical axes of the objective lenses 5 and 6 are coincident with theoptical axes of the eyepieces 9 and 10 bent by 180° by the second Porroprisms 7 and 8.

Here, planes in which the optical axes of the respective objectivelenses 5, 6 are located and are perpendicular to the horizontal planeare referred to as vertical planes.

The first Porro prisms 3 and 4 are arranged such that the firstreflecting surfaces 3 a, 4 a and the second reflecting surfaces 3 b, 4 bare perpendicular to the vertical planes, respectively. The optical axesof the objective lenses 5 and 6 intersect the centers of the secondreflecting surfaces 3 b and 4 b at 45° and are bent by a right angletoward the first reflecting surfaces 3 a and 4 a. The optical axes bentby the second reflecting surfaces 3 b and 4 b are again bent by thefirst reflecting surfaces 3 a and 4 a at a right angle in the respectivevertical planes. Therefore, the optical axes of the objective lenses 5and 6 are bent by 180° in the respective vertical planes by the firstPorro prisms 3 and 4.

With above described arrangement, incident optical axes, which are theoptical axes of the objective lenses 5 and 6 bent by 180° by the firstPorro prisms 3 and 4, are parallel to exit optical axes, which are theoptical axes of the eyepieces 9 and 10 extended toward the eye points.

Object light rays incident on the first Porro prisms 3 and 4 arereflected by the first reflecting surfaces 3 a, 4 a and the secondreflecting surfaces 3 b, 4 b in succession, and then the object lightrays are incident on the respective objective lenses 5 and 6. Imagesformed by the objective lenses 5 and 6 are inverted real images.However, since the first Porro prisms 3 and 4 invert the orientations ofthe object light rays in the vertical direction, and the second Porroprisms 7 and 8 invert the orientations of the object light rays in thehorizontal direction, the erected images can be observed through theeyepieces 9 and 10.

In the first embodiment, since the objective lenses 5 and 6 are locatedbetween the second reflecting surfaces 3 b, 4 b and the third reflectingsurfaces 7 a, 8 a, the distance between the objective lenses 5, 6 andfield stops can be shorter than the conventional optical system, whichenables to decrease the focal lengths of the objective lenses 5 and 6without narrowing the space for the erecting systems. Therefore, thebinoculars of the first embodiment can increase the real field of viewwith employing the Porro type erecting system and keeping a compacttotal size.

Second Embodiment

FIGS. 2 through 4 show binoculars according to a second embodiment. Thedifference of the second embodiment from the first embodiment is toemploy mirrors 11, 11 a and 11 b instead of the first Porro prisms 3 and4. The other constructions are common to the first embodiment.

The binoculars of the second embodiment has a pair of telescopes 1 a and2 a that consist of objective lenses 5, 6, eyepieces 9, 10 and Porrotype erecting systems that have a retractable mirror 11, a pair ofsecond mirrors 11 a, 11 b and Porro prisms 7, 8. The second mirrors 11 aand 11 b are located at the same positions of the second reflectingsurfaces 3 b and 4 b of the first embodiment, and are adjacent to eachother in the same plane.

As described above, the Porro type erecting system has first, second,third and fourth reflecting surfaces. In the second embodiment, theretractable mirror 11 is a common first reflecting surface to both ofthe telescopes 1 a and 1 b, the second mirrors 11 a, 11 b act as thesecond reflecting surfaces.

Further, the retractable mirror 11 can swing between a working positionwhere the first and second reflecting surfaces are perpendicular and aretracted position where the free end of the retractable mirror 11 movesclose to the second mirrors 11 a and 11 b. That is, the retractablemirror 11 is supported by a casing (not shown) on a hinge (not shown) atthe side of the second mirrors 11 a and 11 b.

FIG. 3 is a side view of the binoculars of the second embodiment whenthe retractable mirror 11 is in the working position. In the workingposition, the reflecting surface of the retractable mirror 11 and thereflecting surfaces of the second mirrors 11 a and 11 b areperpendicular to each other. The optical function of the secondembodiment is the same as the first embodiment. That is, the objectlight rays are reflected by the retractable mirror 11 and the secondmirrors 11 a, 11 b, and then converged by the objective lenses 5 and 6to form real images. The object light rays through the objective lenses5 and 6 are then reflected by the Porro prisms 7 and 8, and aremagnified through the eyepieces 9 and 10.

When the retractable mirror 11 swings to the retracted position as shownin FIG. 4, the retractable mirror 11 is parallel to the horizontalplane, i.e., the retractable mirror 11 forms 45° with respect to thesecond mirrors 11 a and 11 b.

Since the objective lenses 5 and 6 are located between the secondmirrors 11 a, 11 b and the Porro prisms 7, 8, the optical system of thebinoculars becomes thinner in the vertical direction when theretractable mirror 11 is in the retracted position. This is convenientto store the binoculars into a bag and/or to carry the binoculars.

Further, when the first reflecting surfaces of the erecting system isretractable, it is preferable that the first reflecting surfaces of bothtelescopes are formed as a common retractable mirror as described in thesecond embodiment. If independent retractable mirrors are provided inthe telescopes, mechanical error of the retractable mechanisms may causedifference in the directions of the incident optical axes between theright and left telescopes. When the common retractable mirror isprovided, the mechanical error does not cause the difference in thedirections of the incident optical axes.

Third Embodiment

FIGS. 5 through 7 show binoculars according to a third embodiment. Thedifference of the third embodiment from the second embodiment is toemploy mirrors 12 a, 12 b, 13 a and 13 b instead of the Porro prisms 7and 8. The other constructions are common to the second embodiment.

The binoculars of the third embodiment has a pair of telescopes 1 b and2 b that consist of objective lenses 5, 6, eyepieces 9, 10 and Porrotype erecting systems that have a retractable mirror 11, a pair ofsecond mirrors 11 a, 11 b, a air of third mirrors 12 a, 13 a and a pairof fourth mirrors 12 b, 13 b. The third mirrors 12 a and 13 a arelocated at the same positions of the third reflecting surfaces 7 a and 8a in the second embodiment, and the fourth mirrors 12 b and 13 b arelocated at the same positions of the fourth reflecting surfaces 7 b and8 b in the second embodiment.

FIG. 6 is a side view of the binoculars of the third embodiment when theretractable mirror 11 is in the working position. When the retractablemirror 11 swings to the retracted position as shown in FIG. 7, theretractable mirror 11 is parallel to the horizontal plane. The binocularof the third embodiment is also convenient to store it into a bag and/orto carry it.

Fourth Embodiment

FIGS. 8 through 10 show binoculars according to a fourth embodiment. Thedifference of the fourth embodiment from the third embodiment is theposition of the objective lenses 5 a and 6 a. The other constructionsare common to the third embodiment.

The binoculars of the fourth embodiment has a pair of telescopes 1 c and2 c that consist of objective lenses 5 a, 6 a, eyepieces 9, 10 and Porrotype erecting systems that have a retractable mirror 11, a pair ofsecond mirrors 11 a, 11 b, a pair of third mirrors 12 a, 13 a and a pairof fourth mirrors 12 b, 13 b. The objective lenses 5 a and 6 a arelocated between the retractable mirror 11 and the second mirrors 11 a,11 b.

FIG. 9 is a side view of the binoculars of the fourth embodiment whenthe retractable mirror 11 is in the working position. When theretractable mirror 11 swings to the retracted position as shown in FIG.10, the retractable mirror 11 is parallel to the horizontal plane.

Since the objective lenses 5 a and 6 a are located between theretractable mirror 11 and the second mirrors 11 a, 11 b, the opticalsystem of the binoculars becomes thinner in the vertical direction whenthe retractable mirror 11 is in the retracted position. This isconvenient to store the binoculars into a bag and/or to carry thebinoculars.

The binoculars of the embodiments may be provided with an interpupillaryadjusting mechanism that adjusts the interpupillary distance based on adistance between pupils of a user. In such a case, right and lefttelescopes are mounted on separate casings, respectively. The adjustingmechanism should be mounted between the casings to relatively slide thecasings in the horizontal direction. Further, when the binoculars hasthe common retractable mirror, the width of the retractable mirror inthe horizontal direction should be long enough to cover the necessaryportion of the variable incident region that varies depending on theinterpupillary distance.

The present disclosure relates to the subject matters contained inJapanese Patent Applications No. HEI 11-306447 and No. HEI 11-306448,filed on Oct. 28, 1999, which are expressly incorporated herein byreference in their entireties.

What is claimed is:
 1. A telescope, comprising: an erecting systemhaving first, second, third and fourth reflecting surfaces that arearranged from an object side, said first and second reflecting surfacesand said third and fourth reflecting surfaces facing each other at aright angle, respectively, wherein an intersection line between extendedsurfaces of said first and second reflecting surfaces is perpendicularto an intersection line between extended surfaces of said third andfourth reflecting surfaces; an objective lens that is located betweensaid second and third reflecting surfaces, said objective lens having apositive refractive power to converge object light that is reflected bysaid first and second reflecting surfaces for forming an image; aneyepiece that is located between said fourth reflecting surface and aneye point, said eyepiece having a positive refractive power to magnifysaid image formed by said wherein said first reflecting surface isformed on a retractable mirror that can swing between a working positionwhere said first and second reflecting surfaces are perpendicular and aretracted position where the free end of said retractable mirror movesclose to said second reflecting surface.
 2. The telescope according toclaim 1, wherein said third and fourth reflecting surfaces compriseback-surfaces of a right-angle prism.
 3. A telescope as in claim 1, saidretractable mirror controlled by a retracting mechanism comprising anangle adjusting mechanism.
 4. A telescope as in claim 1, wherein anincident optical axis from an object to said first reflective mirror isparallel to an exit optical axis from said eyepiece to said eye point.5. Binoculars comprising: a pair of telescopes arranged side by side,each of said telescopes comprising: an erecting system having first,second, third and fourth reflecting surfaces that are arranged from anobject side, said first and second reflecting surfaces and said thirdand fourth reflecting surfaces facing each other at a right angle,respectively, an objective lens that is located between said second andthird reflecting surfaces, said objective lens having a positiverefractive power to converge object light that is reflected by saidfirst and second reflecting surfaces for forming an image, an eyepiecethat is located between said fourth reflecting surface and an eye point,said eyepiece having a positive refractive power to magnify said imageformed by said objective lens; wherein said second reflecting surfacesof said erecting systems are adjacent to each other in the same plane.6. The binoculars according to claim 5, wherein said first and secondreflecting surfaces of each of said erecting systems compriseback-surfaces of a right-angle prism.
 7. The binoculars according toclaim 5, wherein said third and fourth reflecting surfaces of each ofsaid erecting systems comprise back-surfaces of a right-angle prism. 8.Binoculars comprising: a pair of telescopes arranged side by side, eachof said telescopes comprising: an erecting system having first, second,third and fourth reflecting surfaces that are arranged from an objectside, said first and second reflecting surfaces and said third andfourth reflecting surfaces facing each other at a right angle,respectively, an objective lens that is located between said second andthird reflecting surfaces, said objective lens having a positiverefractive power to converge object light that is reflected by saidfirst and second reflecting surfaces for forming an image, an eyepiecethat is located between said fourth reflecting surface and an eye point,said eyepiece having a positive refractive power to magnify said imageformed by said objective lens; wherein said first reflecting surface ofeach of said erecting systems is formed on a retractable mirror that canswing between a working position where said first and second reflectingsurfaces are perpendicular and a retracted position where the free endof said retractable mirror moves close to said second reflectingsurface.
 9. Binoculars comprising: a pair of telescopes arranged side byside, each of said telescopes comprising: an erecting system havingfirst, second, third and fourth reflecting surfaces that are arrangedfrom an object side, said first and second reflecting surfaces and saidthird and fourth reflecting surfaces facing each other at a right angle,respectively, an objective lens that is located between said second andthird reflecting surfaces, said objective lens having a positiverefractive power to converge object light that is reflected by saidfirst and second reflecting surfaces for forming an image, an eyepiecethat is located between said fourth reflecting surface and an eye point,said eyepiece having a positive refractive power to magnify said imageformed by said objective lens; wherein said first reflecting surfaces ofsaid erecting systems are formed on a common mirror.